The dimensioning of coupling slots for microwave feeding of the kind mentioned above often causes a number of problems. The achievement of good fixing, that is, good galvanic contact, between the feeding waveguide and the cavity wall can be problematic because of inaccessibility for spot welding means which at the time of manufacture have to be inserted into and behind the slot opening in connection with the spot welding of the waveguide to the cavity. As will be appreciated, this leads to constructive limitations.
For technical microwave reasons it is often desirable that the width (so-called a-dimension) of the feeding waveguide be maintained in the whole slot area, despite the fact that the width (a-dimension) of the selected coupling slot is significantly smaller than the a-dimension of the waveguide. This can cause problems with the required spot welding in view of the plate bending desired in connection with manufacturing, as well as with concentrations of conduction current in the cavity wall plate adjacent to the slot in the area between the respective slot ends and the side wall connection associated with the waveguide. The latter is particularly pronounced in connection with simple coupling slots of the so-called H-type and when TE10 mode fields are employed.